Oral cancer is the most common neoplasm of the head and neck with an estimated annual incidence over 300,000 worldwide. Oral leukoplakia is a precancerous lesion with an increased risk of cancer development in oral cavity and therefore, an excellent model for prevention studies. We have shown that many oral leukoplakia are genetic lesions which carry higher risk to progress to cancer. Chemoprevention strategy has proved to be a powerful tool to prevent or delay cancer development in high risk populations. However, intermediate endpoints must be developed to determine efficacy of chemopreventive agents in order to shorten the duration of clinical trials and save resources. We hypothesize that molecular alterations critical in early oral tumorigenesis can serve as biomarkers to accurately predict the risk of oral cancer development and elimination or reduction of such alterations by chemopreventive agents can prevent or delay oral cancer development. We further hypothesize that molecular profiles and responses to chemopreventive agent(s) predict individual's biological efficacy of the agent(s) and therefore, outcomes of the preventive strategy. To test these hypotheses, we plan (1) To determine loss of heterozygosity (LOH) at critical tumor suppressor loci in predicting oral cancer risk prospectively in patients with oral premalignant lesions (OPL). We will determine an added value of LOH to DNA content status in assessing oral cancer risk. (2) To determine the role of aberrant promoter methylation at critical tumor suppressor genes alone or in combination with LOH in predicting oral cancer risk prospectively in patients with OPL. (3) To determine whether COX-2 inhibitor and epidermal growth factor receptor (EGFR) inhibitor alone or in combination can reduce the cell populations with aberrant promoter methylation and therefore reduce oral cancer rate. (4) To determine clonal relationship between OPL and subsequently developed oral cancer/OPL to understand therapeutic role of the chemopreventive agents. (5) To identify novel biomarkers important in cancer risk assessment and reveal novel mechanisms of the chemopreventive agents in vivo using proteomic approaches. The success of the project will establish a panel of validated biomarkers to be used as predictors for oral cancer risk and intermediate surrogates for chemoprevention trials. Novel biomarkers and in vivo mechanisms of the preventive agents used will also be discovered.